1. Field of the Invention
The present invention relates to a transmission heat-development photosensitive material, and more particularly to a photosensitive material which is capable of preventing bleeding of the transmission heat-development photosensitive material.
2. Description of the Related Art
An image recording apparatus for recording a medical image for use in a digital radiography system, a CT, an MR or the like which uses a heat accumulating fluorescent sheet, is known. The foregoing apparatus employs a wet system for obtaining a reproduced image by performing a wet process after an image has been photographed or recorded on a silver-salt photographic photosensitive material.
In recent years, a recording apparatus has attracted attention which employs a dry system in which the wet process is not performed. Also the image recording apparatus adapted to the dry system records an image by irradiating (exposing) a photosensitive material with a laser beam so that a latent image is formed on the photosensitive material. The photosensitive material on which the latent image has been formed is heated so that the latent image is developed. The exposure is usually performed such that scanning (main scanning) with a laser beam is performed while the output of the laser beam is being controlled in accordance with image data obtained from an individual photographing process. As a matter of course, also the photosensitive material is moved in a predetermined direction (sub-scanning).
FIG. 7 shows a heat-development photosensitive material recording apparatus of the foregoing type which is a previous invention filed by the applicant of the present invention. Referring to FIG. 7, an image forming apparatus 10 is an apparatus arranged to use a heat development photosensitive material (hereinafter called a xe2x80x9crecording material Axe2x80x9d) which does not require the wet development process. Moreover, scanning exposure using laser beam L is performed to expose the recording material A to correspond to a required image so that a latent image is formed. Then, heat development is performed so that a visible image is obtained. The image forming apparatus 10 comprises a recording-material supply section 12, a width aligning section 14, an image exposing section 16 and heat development section 18 disposed in this order in a direction in which the recording material A is conveyed. The recording-material supply section 12 has two sections having inside portions 22 and 24 to permit selective use of the recording materials A (for example, B4-size recording materials or half-cut recording materials) set in the foregoing sections. The recording material A is a recording material on which an image is recorded (exposed) by the laser beam L and which is developed with heat to develop color. In accordance with a print command, an uppermost recording material A in the magazine 100 selected by suction cups 26 and 28 structured to each sheet is taken out. Then, the recording material A is guided by paired supply rollers 30 and 32, paired conveying rollers 34 and 36 and conveying guides 38, 40 and 42 disposed downstream in the conveying direction so as to be conveyed to the width aligning section 14.
The width aligning section 14 aligns the position of the recording material A with a direction (hereinafter called a xe2x80x9cwidthwise directionxe2x80x9d) perpendicular to the conveying direction. In the downstream image exposing section 16, the width aligning section 14 performs alignment of the recording material A in the main scanning direction, that is, so-called side regist. Then, a conveying roller pair 44 conveys the recording material A to the downstream image exposing section 16.
The downstream image exposing section 16 uses a laser beam to expose the recording material A to correspond to the image, the image exposing section 16 incorporating an exposing unit 46 and a sub-scan conveying means 48.
FIG. 8 shows an example of the image exposing section 16.
Referring to FIG. 8, the image exposing section 16 incorporates:
(1) a first laser-beam source 50 having a semiconductor laser 50a for emitting laser beam L0 having a wavelength serving as a reference for a recording operation, a collimater lens 50b for converting the laser beams into a parallel luminous flux and a cylindrical lens 50c; and
(2) a second laser-beam source 200 having a second semiconductor laser unit 200a for emitting laser beam L1 in a direction perpendicular to the direction of the optical axis of the first laser-beam source 50 and having a different wavelength from that of the first laser beam, a collimater leans 200b and a cylindrical lens 200C. Light emitted from each of the laser-beam sources 50 and 200 is allowed to pass through a polarizing beam splitter 202 so as to be formed into superimposed beams having the same phase. Then, the beams are allowed to pass through a reflecting mirror 204 so as to be made incident on a polygonal mirror 54. When the polygonal mirror 54 is rotated, the laser beam is applied in a main scanning direction b through a fxcex8 lens 56 and a cylindrical mirror 58 while the laser beam is being polarized.
In response to an input image signal, a control unit (not shown) operate a driver 52 so as to rotate a conveying motor 206 provided for a polygonal mirror (a rotative polygonal mirror) 54 and a roller pair 62. Thus, while the recording material A is being scanned in the main scanning direction b with the laser beam, the recording material A is conveyed in a sub-scanning direction a.
The foregoing superimposed-wave optical system is an example. As a matter of course, the present invention is not limited to the foregoing system. Although semiconductor laser beam is employed in the foregoing description, the present invention is, as a matter of course, limited to this. Another laser beam, for example, Hexe2x80x94Ne laser beam may, of course, be employed.
As a result, while the recording material A is being sequentially conveyed in the sub-scanning direction by the sub-scanning direction by the conveying motor 206 provided for the roller pair 60 and 62, a latent image having a predetermined outline is formed on the surface of the recording material A in the main scanning direction.
Referring again to FIG. 7, then, the recording material A caused to have the latent image formed by the image exposing section 16 shown in FIG. 8 is conveyed to the heat development section 18 by conveying roller pairs 64, 66 and 132. The heat development section 18 is a section for heating the recording material A to perform the heat development to convert the latent image into a visible image. A plate heater 320 accommodated in the heat development section 18 includes a heating member which is a plate-like heating member including a heating member, such as a nichrome wire, which is laid flatly. Thus, the development temperature for the recording material A is maintained. As shown in the drawing, the plate heater 320 projects upwards. Moreover, there are provided a supply roller 326 serving as a conveying means for relatively moving the recording material A with respect to the plate heater 320 while making the recording material A contact with the surface of the plate heater 320; and a pressing roller 322 which transmits heat from the plate heater 320 to the recording material A and disposed adjacent to the lower surface of the plate heater 320. Moreover, a heat insulating cover 325 for maintaining the temperature is disposed opposite to the plate heater 320 of the pressing roller 322.
As a result of the foregoing structure, the recording material A passes through a space between the pressing roller 322 and the plate heater 320 by dint of the conveying rotations of the supply roller 326. Then, the heat treatment is performed so that the recording material A is developed with heat. Then, the exposure process is performed so that the recorded latent image is converted into a visible image. Since the conveyance is performed such that the leading end is pressed against the plate heater 320, buckling of the recording material A can be prevented.
Although the plate heater has been described, the present invention is not limited to this. A means which uses another heat development method, for example, a heat drum+belt type means may, of course, be employed.
The recording material A discharged from the heat development section 18 is, by a conveying roller pair 140, guided to a guide plate 142. Then, the recording materials A are accumulated in a tray 146 through paired discharge rollers 144.
The heat development photosensitive material, which is the recording material A, will now be described.
FIG. 6 is a curvature showing a heat development photosensitive material. Referring to FIG. 6, the material incorporates, when viewed from the surface on which the laser beam L is made incident (from the upper portion of the drawing), a surface protective layer for protecting an image forming layer and preventing adhesion; the Em (emulsion) layer; a support-member layer (usually made of PET); and a back layer (and an AH (antihalation) layer in some cases).
The Em layer is an image forming layer formed on the surface of the support layer on which the laser beam L is made incident and containing a binder composed of latex at a ratio of 50% or higher and a reducing agent which is organic silver salt. When the image forming layer is exposed to incident laser beam L, a photocatalyst, such as photosensitive silver halide, forms a core for a latent image. When the core of the latent image is heated, the action of the reducing agent moves silver of the ionized organic silver salt so as to be bonded with the photosensitive silver halide and formed into crystal silver with which an image is formed. As the organic silver salt, silver salt of an organic acid, preferably silver salt of long-chain fatty carboxylic acid having 10 to 30 carbon atoms and organic or inorganic silver salt, the ligant of which has a stability factor coefficient of complex of 4.0 to 10.0 are exemplified. Specifically, the following materials are exemplified: silver salt of behenic acid, silver salt of arachidic acid, silver stearate, silver olerate, silver laurate, silver caproate, silver myristate, silver palmitate, silver maleate, silver fumarate, silver tartrate, silver linoleate, silver butyrate and silver camphorate. The image forming layer of the recording material contains a material, for example, photosensitive silver halide (hereinafter called xe2x80x9csilver halide) which is converted into a photocatalyst after it has been exposed to light.
The image forming layer of the recording material or another layer on the same surface of the image forming layer may contain an additive which is known as a tone adjuster in a preferred quantity of 0.1 mol % to 50 mol % with respect to one mol of silver to raise the optical density. Note that the tone adjuster may be a precursor induced to have an effective function only when the development process is performed. The tone adjuster may be any one of a variety of known tone adjusters for use in the recording material. Specifically, the following materials are exemplified: a phthalimide compound, such as phthalimide or N-hydroyphthalimide; cyclic imide, such as succinimide, pyrazoline-5-on; naphthalic imide, such as N-hydroxy-1, 8-naphthalic imide; cobalt complex, such as cobalt hexamine trifluoroacetate; mercaptan, such as 3-mercapto-1,2,4-triazole or 2,4-dimercaptopyrimidine; phthalazinone derivative, such as 4-(1-naphtyl) phthalazinone; and its metal salt. The foregoing tone adjuster is added to the solution, which must be applied, as solution, powder or dispersed solid particles.
The sensitizing coloring matter must be capable of spectrosensitizing silver halide in a required wavelength region when the sensitizing coloring matter has been adsorbed to silver halide particles. To add the sensitizing color matter to the silver halide emulsion, it may directly be dispersed in the emulsion or it may be dissolved in single or a mixed solution of water, methanol, ethanol, N, N-dimethylformamide or the like, followed by adding the solution to the emulsion.
The surface protective layer is formed by an adhesion preventive material exemplified by wax, silica particles, elastomer-type block copolymer containing styrene (styrene-butadiene-styrene or the like), cellulose acetate, cellulose acetate butylate and cellulose propionate.
When the halation preventive dye is employed, any compound capable of satisfying the following requirement may be employed: the dye must be capable of performing required absorption in the wavelength and; the absorption must sufficiently be restrained in the visible region after the process has been completed; and a preferred absorbance spectrum shape of the antihalation layer can be obtained. Although the following materials are exemplified, the material is not limited to the following materials.
As a single dye, compounds disclosed in Japanese Patent Laid-Open No. 7-11432 and Japanese Patent Laid-Open No. 7-13295 are exemplified. As dyes which perform decoloration by carrying out processes, compounds disclosed in Japanese Patent Laid-Open No. 52-139136 and Japanese Patent Laid-Open No. 7-199409 are exemplified. It is preferable that the foregoing recording material has the image forming layer on either surface of the support member and a back layer on another surface.
To improve conveyance easiness, a matting agent may be added to the back layer. In general, the matting agent is in the form of particles of organic or inorganic compound which is dissoluble in water. The preferred organic compound is exemplified by water dissoluble vinyl polymer, such as polymethylacrylate, methyl cellulose, carboxy starch and carboxy nitrophenyl starch. The preferred inorganic compound is exemplified by silicon dioxide, titanium dioxide, magnesium dioxide, aluminum oxide and barium sulfate.
The binder for forming the back layer may be any one of a variety of colorless, transparent or semitransparent resins. The resin is exemplified by gelatin, arabic rubber, polovinyl alcohol, hydroxyethyl cellulose, cellulose acetate, cellulose acetate butylate, casein, starch, poly (metha) acrylate, polymethylmethacrylate and polyvinyl chloride.
It is preferable that the back layer is a layer, the maximum absorption is 0.3 to 2 in a required wavelength range. If necessary, the halation preventive dye for use in the foregoing antihalation layer may be added to the back layer.
When visible light is used to record an image on a photosensitive material having an exposing wavelength of 750 nm or shorter which is included in a visible region, required sharpness must be maintained to prevent halation and irradiation. To achieve this, visible-light absorbing dye which is an additive known as the color adjuster is employed. When the color developed by the foregoing dye is left at a high density in a case of a transmission-type material for use in a medical purpose or a printing purpose, there arises a problem in that a satisfactory quality cannot be realized. When, for example, recording in red is performed, cyan pigment for absorbing red is added to the photosensitive material. If the quantity of the cyan pigment is too large, excessive development of blue raises a problem. Therefore, the adsorbance of the dye must be lowered or a post process after the exposure must be performed to decolor the excessive color. Specifically, the post-process is performed by using a material obtained by adding pigment of a type which disappears with heat to the photosensitive material to cause the pigment to disappear with heat during the heat development. Since the dye enlarges the cost, minimizing the initial adsorbance has been performed. When the adsorbance of the dye is lowered, a process of recording a void Japanese character having a meaning corresponding to xe2x80x9cwhitexe2x80x9d in a black ground as shown in FIG. 1(A) results in bleeding to occur in the boundary of the white character as shown in FIG. 1(B). As a result, the white character cannot clearly be formed in the black ground.
When a black ground is recorded in a half tone portion as shown in FIG. 2(A), the half tone portions adjacent to the black ground encounters bleeding, as shown in FIG. 2(B). The reason why the foregoing bleeding phenomenon occurs has been detected as follows.
That is, referring to FIG. 6 which is a curvature showing a photosensitive material, a process for recording a half tone image (the left-hand portion of the drawing) is recorded adjacent to a black ground (the right-hand portion of the drawing) will now be considered. Although laser beam L1 having required exposing energy to form a required half tone is sufficient to sensitize the Em layer, laser beam L2 having recording energy for the adjacent black portion as shown in the drawing is reflected by a plurality of positions of the backlayer. Thus, a portion of the laser beam L2 is transmitted to the Em layer adjacent to the half tone portion, causing the Em layer to be sensitized.
To solve the above-mentioned problem, an object of the present invention is to provide a photosensitive material and a recording method is free from bleeding in a boundary when a void image is formed in a black ground or when a black ground is recorded in a half tone portion.
To solve the above-mentioned problem, according to an aspect of the present invention, there is provided a transmission heat-development photosensitive material having a structure that an adsorbance of the material with respect to an exposing wavelength before an exposure and development process is 0.5 or smaller and a highest density of 2.8 can be realized with energy which is not larger than 7 times (in a case of a negative-type material) exposing energy required to realize a density of 1.2 or not smaller than {fraction (1/7)} (in a case of a positive-type material) of the exposing energy.
According to another aspect of the present invention, there is provided a transmission heat-development photosensitive material having a property that an adsorbance of the material with respect to an exposing wavelength before an exposure and development process is 0.5 or smaller and a highest density of 2.8 can be realized with energy which is not larger than 25 times (in a case of a negative-type material) exposing energy required to realize a lowest density +0.1 of the photosensitive material or not smaller than {fraction (1/25)} (in a case of a positive-type material) of the exposing energy.
As described above, the photosensitive material is specified which is capable of forming a white image in a black portion (a lowest density) and/or a halftone image in a black portion (a highest density) in a state in which the hard gradation to a degree at which conspicuous irregurality in scanning can be prevented, is employed.
When the foregoing photosensitive material is employed, the difference between the exposing energy required to form a halftone image and the exposing energy required to realize the highest density with which a black image is formed can appropriately be reduced. Therefore, the contribution ratio of the halation caused from reflection from the backlayer can be lowered. Thus, bleeding in the boundaries can be prevented.